z axis driven pump: pressure regulation /logic input question

[moorea21]

Hi,

I have a plotter that uses incremental movement of the 'z' axis to drive a material deposition pump. (Another axis (A) causes a small piston to oscillate and print the material onto a flat surface.) I had originally wanted to use the spindle drive for driving the pump, but my ncPod controller does not do spindle control, apparently.

There is a slight problem with pressure regulation, which I intend to solve by fitting a load cell, with circuitry to generate a logic 1 when the pressure falls below a predetermined value, and logic 0 when pressure is satisfactory. I hope to use the logic 1 signal to start the pump (ie cause the z axis to step), and logic 0 to shut it off again, thereby achieving pressure regulation.

Is there a way in Mach 3 to start/stop an individual axis in response to a logic input? It might be a bit like giving an Estop signal to just the one axis.

Does anyone know if Mach can do this? Or should I think about putting an Arduino on the machine to control the z axis seperately to Mach 3? Bear in mind that the z axis s not being used to position anything, just to provide pump presssure. The actual printing is done by the A axis, which must remain under mach control.

Any ideas?

Rich

[moorea21]

I've just thought:-

If I write a VB module that works like:-

Do until input1 =0  'ie do until the pressure reaches minimum value, triggering logic1 from pressure sensor circuit
          G01 Z(Z+1)  ' ie increment Z (pump) until correct pressure is reached

can I call it in the Gcode and have it run in the background for as long as the machine is on? I'm sure the syntax is way off; this is just really to describe how it might function.
I haven't used VB with Mach before, in fact I only started to learn VB about 2 weeks ago, so if someone could tell me if I'm on the right track or not, that would be great

Thanks,

Richard B

[moorea21]

I seem to have mistyped; should be:

Do until input1 =0  'ie do until the pressure reaches minimum value, triggering logic 0 from pressure sensor circuit
          G01 Z(Z+1)  ' ie increment Z (pump)

that's better!

[Tweakie.CNC]

Richard,

You are on the right lines.

The Macro Pump runs in the background and could control the functions you require with your VB code.
Here is one link but there are many if you do a search  http://www.machsupport.com/forum/index.php/topic,13576.0.html

Tweakie.

[Hood]

I am not sure if this will work as I dont think you will be able to switch an axis on and off whilst other axis are running.
You could possibly do it by having the move in each line of your code but having a physical relay controlling whether the axis actually gets the steps or not. That would then maybe lead to other problems in that that axis motion would be taken into consideration by Mach when doing a move.
The best solution may be to externally drive the axis somehow by using the macropump to switch on/off a pulse generator.

Hood

[poppabear]

another option might be, to swap out your Z axis stepper, with some kind of straight motor, with on/off control, have your load cell trigger the Motor on, and off.

another option (depending on how much money you want to do), you could just set an Air Pressure cylinder and set the pressure for that cylinder to what you need your compressor would keep that amount. you could user your current pressure cell to drive the on/off of the solinoid that would open close your piston to push your stuff.

you could use other options as well, analog devices with modbus, or other things like PoKeys, etc., I guess it all depends on if you makeing money with the machine or not.

I think cutting on/off the Z axis while mach thinks it is running, your going to run into accel/decel probs..

scott

[Hood]

I think cutting on/off the Z axis while mach thinks it is running, your going to run into accel/decel probs..

scott

Scott, yes that was my concern doing it that way, you would have to have the feed set so that switching on.off the pulse didnt stall the stepper which in turn would impact on the other axis.

Hood

[Tweakie.CNC]

Rich,

I made the assumption that your plotter Z axis is just 'pen up' / 'pen down' and operates the pump from one of these two conditions - is this the case ?

Tweakie.

[stirling]

If I understand correctly - you want the Z to be driven at some fixed rate under the control of your logic signal and independantly of the "commanded" axes.

A possible way of doing this is to use Mach's THC. If your logic signal is wired to THC down (say) then as long as your signal is active Z will move down and will stop when your signal goes inactive - completely independantly of X and Y motion.

You will of course need to modify your screen set to include the THC control.

Ian

[kf2qd]

Sounds like you just need an output on/off. 

If i understand correctly - you are extrududing some material - you need to extrude at some pressure. It sounds like you need to have a signal for extrude on/off and then let the pressure control be part of the extruder and don't worry about it being an axis. Axis's are for motin in the X Y & Z planes. Is the extrusion amount in any way deopendent upon what Z & Y are doing, or are they supposed to be programmed so that they are moving at the proper speed so you get the correct deposition?

Otherwise you are going to have to always be moving Z in large enough moves so that it can provide enough volume to exceed the pressure which would be better done with just on/off control.